This invention relates to electrical circuit makers and breakers that are cam-operated and more specifically to the general structure and method of manufacturing cam-operated appliance timers.
Cam-operated timers have been used for years to control the functioning of appliances such as clothes washing machines, clothes dryers, and dishwashers. Cam-operated timers used in appliances operate to control various appliance functions in accordance with a predetermined program. Examples of appliance functions that can be controlled by a cam-operated timer are: agitation, washing, spinning, drying, detergent dispensing, hot water filling, cold water filling, and water draining.
Cam-operated timers typically have a housing with a control shaft that serves as an axis of rotation for a drum-shaped cam which may be referred to as a camstack. The camstack is connected to a drive system that is powered by an electric motor to rotate the camstack. Camstack program profiles or blades carry the control information to operate blade switches. When the camstack rotates, the cam blades are engaged by switches that open and close in response to the cam blade program. A knob is generally placed in the end of the control shaft which extends through the appliance control console for an appliance operator to select an appliance program.
Cam-operated timers are complex electromechanical devices having many mechanical components interoperating with each other under close tolerances. One of the primary reasons that previous cam-operated timer have not been assembled with a great deal of automation equipment is that the timer design requires components to be assembled from a variety of axes. Manual assembly of a complex device such as a cam-operated timer compared to automated assembly can require more time and generate more quality defects. Automated assembly of a cam-operated timer is desirable because automated assembly should be quicker and have less quality defects than can be achieved economically with manual assembly.
Some previous cam-operated timers have employed a metal housing to contain timer components. The metal housing is typically formed from two or more pieces of sheet metal that are fastened together to form a partially enclosed housing. A metal housing is typically required to be electrically insulated from the appliance and also typically requires connection of a grounding strap. Additionally a metal housing does not dampen the clicking sounds that can be generated by a cam-operated timer's drive or cam followers. The partially enclosed housing can permit contaminates such as dust or lint to enter the cam operated timer and interfere with electrical contacts or other mechanical components. Since the metal housing is typically formed from two or more pieces of metal, maintenance of close component tolerances in relation to each other can be difficult. An example of a metal enclosure is disclosed in U.S. Pat. No. 4,228,690 issued to Ring.
Some previous cam-operated timers designed for relatively simple applications, such as a refrigerator freezer defrost timer, have employed a plastic housing to contain timer components. An example of a plastic enclosure for a cam-operated timer that does employ a small camstack is disclosed in U.S. Pat. No. 4,636,595 issued to Smock et al. An example of a plastic enclosure for a cam-operated timer that does not employ a camstack, but a pancake cam, is disclosed in U.S. Pat. No. 4,760,219 issued to Daniell et al.
Cam-operated timers are typically installed in appliance consoles where space can be very limited with fasteners. A ground strap is usually run from the cam-operated metal housing to the appliance console. A cam-operated timer requiring separate fasteners and a ground strap is difficult for an appliance manufacturer to automate installation of the cam-operated timers into their appliance.
Previous cam-operated timers have been tested for proper operation by connecting the timer switches to an electrical analysis device, directing current through the timer's motor, and allowing the gear train to drive the camstack which then operates the switches of the timer. If the electrical characteristics of the timer match predetermined criteria, then the timer passes the test and is ready for sale. The amount of time that is required for a typical timer to complete a revolution of its camstack when driven by its motor and gear train is often in excess of one hour. This means that the testing time for previous cam-operated timers is also in excess of one hour.